Less Chewing, More Doing

Food processing in early hominid populations might have played a key role in human evolution by increasing net energy uptake, researchers show.

By Catherine Offord | March 11, 2016

WIKIMEDIA, MICHAEL C BERCHAlthough cooking only took off around 500,000 years ago, human use of tools to process food is thought to have been widespread much earlier. Now, a study from researchers at Harvard University suggests that food processing was key in hominid evolution as a means to increase energy intake while reducing energy expenditure. The findings were published in Nature on Wednesday (March 9).

“By processing food, especially meat, before eating it, humans not only decrease the effort needed to chew it, but also chew it much more effectively,” said study coauthor Katie Zink of Harvard University in a statement. “Using stone tools to process food apparently made possible key reductions in the jaws, teeth and chewing muscles that occurred during human evolution.”

Zink and her colleagues attached sensors to the faces of volunteers to record muscle contractions during chewing. The researchers then fed participants goat meat or root vegetables like yams and beets, that were either raw or had been processed by slicing, pounding, or cooking. After chewing as long as seemed necessary for swallowing, each participant spat out the food for analysis.

“What we found was that humans cannot eat raw meat effectively with their low-crested teeth,” said study coauthor Daniel Lieberman in the statement. “But once you start processing it mechanically, even just slicing it, the effects on chewing performance are dramatic.” The researchers calculated that if early humans processed food in a similar way, they could have spent 17 percent less time chewing, with 26 percent less force, than if they had eaten unprocessed food.

“It kind of fills in a gap,” Henry Bunn of the University of Wisconsin-Madison told Smithsonian. “For years people have said, well, there’s a package of biological adaptations that relate to a marked change in diet. Larger brains, larger body size, smaller teeth and a smaller gut all point in the same direction: more meat and better means to obtain it.”

However, Katharine Milton of the University of California, Berkeley, told Smithsonian that the study addressed only a small portion of the ancient diet. “While it’s fun to speculate,” she said, “I am not sure that quantifying the energetics of chewing beet root versus goat meat in itself sheds too much light on the energetics of evolving humans.”

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Zink & Lieberman (1) beautifully illustrate how stone tools could have facilitated Lower Palaeolithc meat-eating, but there's evidence for an intermediate phase in the transition of Homo from a more ape-like diet to partial meat-eating. It has been argued (2–5) that the combination of brain expansion, smaller dentition, reduced chewing musculature (MYH16 inactivation) & reduced gut is no paradox, but is easily explained by early-Pleistocene Homo trekking intercontinentally along African & Eurasian coasts (at least as far as Dmanisi in Georgia, & Mojokerto on Java), where their littoral diet consisted for an important part of shellfish. Generally, ground-dwelling mammals have smaller brains than equally large arboreal relatives, and carnivores don't have relatively larger brains than omnivores, but most littoral & aquatic species have much larger brains than their equally large terrestrial relatives. All great apes use tools, and when sea-levels dropped during the Pleistocene glacials (begin 2.588 Ma), hominid "apes" (tool-using, intelligent, dextrous) were ideally preadapted to colonise the new & expanding econiches on the vast continental shelves. Shell- & crayfish are richest in essential & brain-specific nutrients: docosaenoic acid DHA, taurine, iodine & selenium (2,3), and can best be opened with hard tools, e.g. oyster shells & stones (6). From the coasts, archaic Homo populations soon (begin-Pleistocene?) ventured inland along the rivers, possibly at first seasonally. Followed the rivers inland, they began using the shells & stone tools that they had learned to use to open shellfish at the coast (6–9) also to butcher the carcasses of herbivores near inland waters. Soon, they even might have killed prey hindered in its movements in wetlands, amid reed & in mud. The paleontological record may be taphonomically biased towards stones & bones, which leave more archaeological traces than plant foods & shellfish, and towards inland find sites of butchering compared to coastal feeding, since inland butchering sites were typically riverside, whereas coastal butchering sites have mostly been destroyed by waves, tides, tsunamis & Pleistocene sea-level changes. Although shellfish was probably mostly consumed in situ (leaving few or no traces), several Lower Palaeolithic coastal sites suggesting shellfish consumption have been preserved (6–9). This coastal dispersal scenario (4,5) also helps explain, (a) Zink & Lieberman's experiments on stone tools & meat-eating (1), (b) Homo's transition, in small evolutionary steps, towards partial meat-eating, (c) why cooking was initially unnecessary, and even (d) why "the origins of the genus Homo are murky" (1): Homo's early-Pleistocene coastal dispersal on the then exposed continental shelves left few fossil & archaeological traces.

Meat eating animals just shear and swallow meat while humans have to chew their meat in order to digest it properly. This is demonstrated through the teeth of our ancestors preserved in sedimentary soil of Africa between 4 and 2 million